1. Technical Field
The present invention relates generally to an electric heater for an internal combustion engine and, more particularly, to an electric heater for a positive crankcase ventilation system of an internal combustion engine.
2. Discussion
Positive crankcase ventilation (PCV) draws and feeds gases from the engine crankcase into the engine induction system such as at the intake manifold. Crankcase gases oftentimes include a fairly high percentage of unwanted constituents, such as hydrocarbons, resulting from blowby during engine operation. These unwanted constituents may be burned off after recirculation through the PCV system. A PCV valve normally positioned proximate to the crankcase regulates the flow through the PCV system into the intake manifold in relation to the engine load.
During cold weather operation of the engine, condensation problems can result in the area where the PCV system discharges gases into the intake manifold. More particularly, ambient air drawn into and through the air intake system during operation of the engine mixes with the PCV gases that have been warmed through combustion. Condensation occurs as the PCV gases cool in the mixing zone. If the ambient temperatures are sufficiently cold, the condensed liquid may freeze causing plugging of the PCV system and over-pressures in the crankcase that ultimately may prevent proper engine operation.
Previous PCV heaters have failed to adequately address these freeze-up concerns. More particularly, a presently used PCV heater includes a stamped steel fitting having a steel cup integral with a steel tube. The steel cup is configured to be coupled to an appropriately sized opening in the intake manifold and the steel tube is connectable to a conduit that conveys the ventilated gases from the PCV valve to the fitting. In this device, the tube is heated by a resistance element that is wound about the base of the tube. The resistance element is generally turned twice about the tube and crossed over itself in close proximity to a previous turn. The conductive nature of the cup and tube as well as the proximity of the wires create an undesirably large frequency of shorting.
In heaters having a wrapped resistance wire as the heating element, design concerns specifically related to space constraints, heating capacity, power usage, and short circuiting must be balanced. In general, it would be desirable to optimize the number of wire turns to control the heating capacity of the unit. However, space constraints limit the number of turns that may be used without incurring an unacceptably high frequency or probability of shorting. A smaller diameter wire could be used to decrease the number of turns and improve on shorting. However, when smaller diameter wires are used, the total length of wire is shortened and the operating temperature within the wire is increased leading to a decrease in robustness and service life.
In addition to the above-described operational concerns, the previous heater is difficult to manufacture. More particularly, manufacture requires termination of the resistance wire to lead wires communicating with a power source, manually wrapping wires about the tube, over-potting the wrapped wires with a heat transfer epoxy, allowing the potting epoxy to cure for 30 to 45 minutes, covering the helically wound resistance element with a silicon epoxy to limit electrical conductivity and heat transfer away from the tube, and oven curing the silicon epoxy for 60 minutes. Oftentimes shorting concerns require dipping of the resistance wires in a soft cure heat transfer epoxy prior to wrapping. The epoxy is then cured for approximately thirty (30) to forty-five (45) minutes. This labor intensive and time consuming procedure increases manufacturing costs and limits the capacity of manufacture.
In view of the above, a need exists for an improved PCV heater. Improved PCV heaters would advantageously address each of the above concerns including a reduced frequency of shorting, more simplified and inexpensive manufacturing procedures, concentrate the heat in the area of freeze-up, thermally isolate the heat sink of the heater from the engine, and generate a given amount of heat with better efficiency thereby lowering required wattages and saving energy.